High blood pressure affects nearly one in three Americans leaving them at increased risk for heart attack and stroke. High blood pressure is more common among African Americans (41%) than among Whites (29%). The importance of sodium intake in the regulation of blood pressure is well known, and Americans' estimated intakes far exceed current recommendations. The current recommendations for sodium intake are expressed as milligrams per day (hereafter referred to as sodium alone). However, in the most relied upon study in the evidence base, the DASH-Sodium trial-the three levels of sodium in the experimental diets varied according to individual energy needs; that is, the experimental variable was the amount of sodium per calorie of energy intake (hereafter referred to as sodium density). It is still unclear which predicts blood pressure better, sodium alone or sodium density and it is difficult to discern the difference between them on blood pressure because sodium and energy intakes are highly correlated. Interestingly, the DASH-Sodium trial found a greater impact of changes in sodium intake in African Americans than in Whites. Our overarching hypothesis is that sodium density is a better predictor of blood pressure than sodium alone. Specifically, we will determine which is a better predictor of blood pressure, sodium alone or sodium density, using data from three studies with different designs: (1) a randomized, controlled, cross-over feeding trial (DASH-Sodium); (2) a randomized, controlled diet implementation trial (PREMIER); and (3) a nationally representative survey (NHANES). The clinical trials enrolled approximately equal proportions of non-Hispanic white and African American adults, allowing for an assessment of effect modification by race. We will employ novel statistical modeling approaches, including the use of a biomarker, urinary sodium, available in PREMIER and DASH-Sodium, to obtain estimates adjusted for measurement error. We will also adjust for the error attributable to day-to-day variation in intake. In this study, fist, we will determine whether sodium alone or sodium density was more predictive of blood pressure in pre-hypertensive and Stage 1 hypertensive adults in two clinical trials. Second, we will determine whether the effects of sodium alone and sodium density on blood pressure differ between the non- Hispanic Whites and African Americans who participated in these two trials. Finally, we will determine whether the effects of sodium alone and sodium density on blood pressure found in the trials reflect the relationships between sodium and blood pressure in the general US population by using national survey data for all adults, and we will determine whether the effects differ by race. This work will advance the understanding of the relationships of sodium and sodium density on blood pressure and will inform future dietary recommendations, including clinical guidelines for blood pressure control and the Dietary Guidelines for Americans, which is the nutrition policy of the US government. The results have the potential to improve both clinical and public health practices aimed at diet and blood pressure for all American adults.